1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording in which a recording medium is irradiated with near-field light to lower the coercivity of the recording medium for data writing.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of a recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses a technology in which the surface of the core of the waveguide and the surface of the plasmon generator (near-field light generating element) are arranged to face each other with a gap therebetween, so that evanescent light that occurs from the surface of the core based on the light propagating through the core is used to excite surface plasmons on the plasmon generator to generate near-field light based on the excited surface plasmons.
A thermally-assisted magnetic recording head that employs a plasmon generator as a source of generation of near-field light is configured so that the write head unit includes the plasmon generator and a main pole for producing a write magnetic field. The plasmon generator and the main pole are located in close proximity to each other.
Part of the energy of the light propagating through the core is transformed into heat in the plasmon generator. This gives rise to the following problems. First, during operation of the thermally-assisted magnetic recording head, the plasmon generator and its surroundings rise in temperature. As a result, the plasmon generator and its surroundings expand, and thus a portion of the medium facing surface protrudes toward the recording medium. This causes an end of the read head unit located in the medium facing surface to get farther from the recording medium, thereby causing the problem that a servo signal cannot be read during write operation. Further, the temperature rise of the plasmon generator may cause the plasmon generator to be deformed or broken.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses a technology of providing a metallic layer beside the main pole, that is, on opposite sides of the main pole in the track width direction. This metallic layer functions as a heat sink to facilitate dissipation of heat from the plasmon generator. Providing such a heat sink near the plasmon generator allows for suppressing the temperature rise of the plasmon generator.
A heat sink is formed of a material having a high thermal conductivity. Au is a typical material having a high thermal conductivity. However, since Au is relatively soft, forming an entire heat sink of Au gives rise to problems as discussed below.
When the plasmon generator rises in temperature during operation of the thermally-assisted magnetic recording head, the heat sink also rises in temperature. If the entire heat sink is formed of Au, the temperature rise of the heat sink may result in deformation or breakage of the heat sink due to aggregation. Further, if the entire heat sink is formed of Au, the heat sink may be mechanically deformed or broken upon contact of the medium facing surface with the recording medium. When deformed or broken, the heat sink becomes unable to fully perform its function. As a result, there arise the foregoing problems associated with the temperature rise of the plasmon generator. Thus, a thermally-assisted magnetic recording head including a heat sink that is formed entirely of Au has the drawback of being low in reliability.